The invention relates to an optical record carrier comprising a track for carrying data encoded in optical marks, a parameter of the track having a periodic variation for generating a varying signal when scanning the track, which track comprises reference elements interrupting the periodic variation.
The invention further relates to a device for scanning the optical record carrier, which device comprises a head and control means for scanning the track.
The invention further relates to a method for manufacturing the optical record carrier.
Such a record carrier and apparatus are known from U.S. Pat. No. 5,682,365 (PHN 9666). The document discloses a record carrier in the form of an optical disc having a recording area comprising a pattern of grooves on a substrate, constituting a pattern of circular or spiral tracks for carrying data digitally encoded in optical marks. A parameter of the tracks has a periodic variation, for example the width or the radial position, usually called wobble. The recording tracks are subdivided in longitudinal direction into track portions alternating with reference elements, e.g. headers comprising pre-recorded address marks. The pattern of tracks and headers are made during manufacture, e.g. in the form of a so-called pre-groove and pre-pits formed by embossing. The address marks represent position information for positioning a recording head on a desired track and are indicative for the address of the recording area following the address area. The record carrier is manufactured by first creating a master disc and thereafter replicating the disc. The groove may be formed in the master disc by applying a photo-resist layer on a substrate, expose it with the required pattern and etching unwanted material away. The remaining, intermediate surface is usually called land. The apparatus comprises an optical system for scanning the track for recording or reading information by generating a spot via a radiation beam on the track. The optical disc is rotated and the spot is positioned in radial direction on the center of the track by control means for scanning the track. During scanning a varying signal is generated corresponding to the periodic variation of the track. The varying signal is used to control the speed of the scanning. In a standardized recording system of a record carrier and a scanning device the radiation beam generates tracking signals in dependence of the geometric shape of the pre-groove, which tracking signals are processed in a predefined way in the device. The shape is determined by the manufacture process of the record carrier. Hence the standardized system sets fixed requirements for the manufacture process of the record carrier.
It is an object of the invention to provide a record carrier and a scanning device arranged for a more flexible record carrier manufacture process.
For this purpose a record carrier as described in the opening paragraph is characterized according to the invention in that the phase of the periodic variation after the reference elements is indicative of a property of the record carrier for controlling the scanning of the record carrier in dependence of said property. Further a scanning device as described in the opening paragraph is characterized in that the device comprises phase detection means for detecting the phase of the periodic variation after the reference elements and setting means for setting the control means in dependence of a property of the record carrier indicated by said phase. For a specific type of record carriers said phase is defined by selecting a positive direction for the periodic variation and determining the direction of the first half of the first instance of the periodic variation after the reference element. More in detail the phase may be determined in relation to a zero point defined in the periodic variation. The invention has the effect, that at least one property of the record carrier may be freely selected, and that the device may easily detect the selected property by detecting the phase of the periodic variation. Then the device sets the control means via the setting means based on the indicated property. Being able to select and indicate a property has the advantage that the manufacture process of the record carrier is more flexible.
The invention is also based on the following recognition. The reference elements are easily detectable in a scanning device, even without optimal setting of the scanning control means. Also the phase of the periodic variation in the track can be detected easily, because the corresponding varying signal has a relative low frequency when compared to read signals of the address marks or recorded marks representing digital data, and therefore setting of the scanning control means is less critical. For correctly reading said marks the scanning system must be fully operational, and therefore said marks cannot be used to transfer information for setting the scanning control means. Hence the phase of the periodic variation is suitable for indicating a property of the record carrier which influences the scanning signals.
An embodiment of the optical record carrier is characterized in that the track is scannable by a scanning beam via an entry side of the record carrier and comprises a groove relative to a surrounding surface, wherein said phase is indicative of whether or not the bottom of the groove is closer to the entry side than the surrounding surface. This has the advantage, that in the record carrier the groove may be an indentation in or a ridge protruding from the surrounding surface, which allows a choice of the number of replication steps. Due to the kind and/or number of steps the bottom of the groove may be closer to entry side of the record carrier or farther away, which is to be indicated by the phase of the periodic variation. A corresponding device is characterized in that the head is arranged for scanning the track by a scanning beam via an entry side of the record carrier and the control means are arranged for performing tracking control in accordance with a tracking signal generated by the head, the track comprising a groove arranged in a surrounding surface, and wherein the setting means comprise controllable inverting means for whether or not inverting the tracking signal in dependence of the detected phase indicating that the bottom of the groove is closer to the entry side than the surrounding surface.
Further advantageous, preferred embodiments of the record carrier and device according to the invention are given in the dependent claims.